Self-renewing cancer stem cells (CSCs) initiate tumours and drive malignant progression by generating and supporting replication of more differentiated non-stem cell progeny. (M. Al-Hajj, et al., Proc Natl Acad Sci USA 100 (7), 3983 (2003); D. Bonnet and J. E. Dick, Nat Med 3 (7), 730 (1997); C. A. O'Brien, et al., Nature 445 (7123), 106 (2007); L. Ricci-Vitiani, et al., Nature 445 (7123), 111 (2007); S. K. Singh, et al., Nature 432 (7015), 396 (2004); T. Schatton and M. H. Frank, Pigment cell & melanoma research 21 (1), 39 (2008)). The mechanisms by which CSCs cause tumour formation and growth and the potential role of CSC-specific differentiation plasticity in tumourigenicity are currently unknown. We recently identified a subpopulation of CSC based on expression of the chemoresistance mediator ABCB5 (ATP-binding cassette, sub-family B (MDR/TAP), member 5) (N. Y. Frank, A et al., Cancer Res 65 (10), 4320 (2005); Y. Huang, et al., Cancer Res 64 (12), 4294 (2004)) within human malignant melanoma (T. Schatton, et al., Nature 451 (7176), 345 (2008)), a highly aggressive and drug-resistant cancer. (T. Schatton and M. H. Frank, Pigment cell & melanoma research 21 (1), 39 (2008); L. Chin, L. A. Garraway, and D. E. Fisher, Genes Dev 20 (16), 2149 (2006).) ABCB5+ Malignant Melanoma Initiating Cells (MMIC) correlate with clinical disease progression and can be specifically targeted to abrogate tumour growth. (T. Schatton, et al., Nature 451 (7176), 345 (2008)). Consistent with these findings, the ABCB5 gene is also preferentially expressed by in vitro self-renewing melanoma minority populations (G. I. Keshet, et al., Biochem Biophys Res Commun 368 (4), 930 (2008)) and by melanoma cell lines of metastatic as opposed to primary, radial growth phase tumour origin (J. F. Sousa and E. M. Espreafico, BMC cancer 8, 19 (2008)).